Four major areas of iron metabolism will be covered in this proposed research project. (1) Characterization of membrane receptor sites for transferrin. Transferrin receptor sites will be isolated from 125I labelled reticulocyte membrane proteins which have been solubilized with non-ionic detergents and separated by immune precipitation of affinity chromatography. Transferrin labelled with ferritin and 55Fe will be utilized in conjunction with autoradiography and electron microscopy to determine whether endocytosis of transferrin is involved in the delivery of iron from the plasma membrane to the mitochondria. (2) The role of transferrin in intestinal iron absorption. In vitro and in vivo studies will be carried out to determine whether binding of transferrin to intestinal epithelial cells plays a role in the control of iron absorption. Alternatively the capacity of the isolated intestinal epithelial cell to synthesize transferrin will be studied by immunologically precipitating transferrin from epithelial cells which have been solubilized with non-ionic detergents after incubation with 3H-leucine. (3) The role of excess iron in the pathogenesis of iron storage disease. Studies will be carried out to determine the mechanism for the increase in prolylhydroxylase activity in rat liver and myocardial cells following iron overload. Total collagen synthesis and turnover will also be measured in these tissues by studying incorporation of 14C proline into collagen and by measuring the disappearance of such labelled collagen over time. (4) Membrane and metabolic abnormalities in iron deficient red cells. The role of iron and its relationship to selenium balance in the maintainance of red cell glutathione peroxidase will be studied. Selenium absorption and excretion will be measured in iron deficient rats in view of the previous demonstration of selenium as a component of glutathione peroxidase. Studies will be carried out to correlate glutathione peroxidase activity, ATP levels and red cell membrane plasticity with abnormalities in the lipid and protein structure of the red cell membrane.